ABSTRACT
A finite element model is developed to study the distortional-lateral torsional interaction buckling behaviour of a structural framing system composed of thin-walled lipped cold formed steel beams. The system consist of purlin sections (transversal members) and frame sections (longitudinal members), both of cold-formed lipped channels, which are connected through their web by thin-walled lipped cold-formed steel angles. This restraining system replaces the fly brackets, which are widely used in the steel construction. No bolting or welding of the top flange of the main channels is done, at the connecting area, because of their destabilizing effects, which may cause premature failure of the channel beams. The main channels are subjected to two concentrated downward point loads, to create a constant bending moment in the middle span. The middle span, which is the focus of this study is chosen to exhibit both distortional and lateral-torsional behaviour. The original model is developed using Abaqus and exported to the Constrained and Unconstrained Finite Strip Method (CUFSM) software in order to isolate the distortional-lateral torsional interaction buckling mode. Geometric imperfections are incorporated in the non-linear finite element model, to determine the failure load of the beams, caused by the interaction buckling modes. The results from the finite element model are compared to the Direct Strength Method (AISI S100-12).
